1. Field of the Invention
The present invention relates to thin-film magnetic heads which are mounted in, for example, hard disk drives. In particular, the present invention relates to thin-film magnetic heads suitable for higher recording densities and higher recording frequencies and relates to methods for making the same.
2. Description of the Related Art
FIG. 9 is an enlarged cross-sectional view of a conventional thin-film magnetic head. This thin-film magnetic head is an inductive head for writing. A MR head for reading may be formed below the inductive head. The thin-film magnetic head has a lower core layer 1 formed of a conventional magnetic material such as permalloy. A gap layer 2 of alumina or the like is formed on the lower core layer 1, and an insulating layer 3 composed of polyimide or a resist material is formed on the gap layer 2.
A coil layer 4 having a spiral pattern is formed on the insulating layer 3. The coil layer 4 is formed of a nonmagnetic conductive material having low electrical resistance, such as copper. The coil layer 4 is covered with an insulating layer 5 formed of polyimide or a resist material. An upper core layer 6 formed of a magnetic material such as permalloy is plated on the insulating layer 5.
The upper core layer 6 faces the lower core layer 1 at a surface opposing a recording medium (air bearing surface (ABS)) and these layers are separated by the gap layer 2. The gap layer 2 forms a magnetic gap with a magnetic gap length GL1 which applies a recording magnetic field to a recording medium. A base end 6b of the upper core layer 6 is magnetically coupled with the lower core layer 1.
In this inductive head, the coil layer 4 yields a recording magnetic field by a recording current flowing therein toward the upper core layer 6 and the lower core layer 1. A magnetic signal is recorded on a recording medium, such as a hard disk, by a fringing magnetic field between the lower core layer 1 and the upper core layer 6 at the magnetic gap.
With trends toward higher recording densities and higher recording frequencies, the saturation magnetic flux density Bs and the specific resistance xcfx81 of the upper core layer 6 must be increased. The specific resistance xcfx81 is an important magnetic characteristic in order to reduce eddy current loss at high-frequencies. However, NiFe alloys, which are generally used in the upper core layer 6, have at most 50 xcexcxcexa9xc2x7cm. As a result, in conventional thin-film magnetic heads, eddy current loss is insufficiently suppressed at high-frequencies.
The high saturation magnetic flux density Bs is a magnetic characteristic which is essential for improved recording density. When the upper core layer 6 is formed of a magnetic material having high saturation magnetic flux density Bs which is suitable for higher recording densities and higher recording frequencies, the specific resistance xcfx81 is further decreased and thus the eddy current loss is unintentionally increased. When the upper core layer 6 is formed of a magnetic material having high specific resistance xcfx81, the saturation magnetic flux density Bs will be be sacrificed to some extent.
The following conventional thin-film magnetic head provides an improved saturation magnetic flux density Bs. In this head, the upper core layer 6 shown in FIG. 9 has two films, that is, a high Bs film having high saturation magnetic flux density Bs and a conventional permalloy film (a NiFe alloy film) in order to be suitable for high recording densities. The lower core layer 1 is composed of only a permalloy film.
Since a recording magnetic field is generated from a portion which is near the gap layer 2 of a leading edge 6a of the upper core layer 6 toward the lower core layer 1, the high Bs film is believed to intensively generate the magnetic field near the gap and this is suitable for future higher recording densities.
This double-layer structure can improve recording characteristics compared to the above single upper core layer 6 composed of permalloy. However, a recording magnetic field formed between the high Bs film and the lower core layer 1 is affected by a magnetic field from the recording medium, and an intensive recording magnetic field will not be concentrated near the gap. As a result, this structure cannot effectively improve an overwrite (OW) characteristic and a non-linear transition shift (NLTS) characteristic, as described in detail below.
The NLTS exhibits a phase lead by nonlinear distortion of a magnetic field generated at the magnetic gap between the upper and lower core layers 1 and 6, respectively, which is caused by a recorded magnetic field from magnetic signals recorded immediately before on the recording medium toward the head.
In order to evaluate the OW characteristic, low-frequency signals are recorded and then high-frequency signals are overwritten. The OW characteristic is evaluated by a decrease in residual output of the low-frequency recorded signals after the high-frequency overwriting compared to the recorded signals after low-frequency recording.
Moreover, this double layer structure does not effectively reduce eddy current loss which is caused by increased recording frequencies.
It is an object of the present invention to provide a thin-film magnetic head including an upper core layer and a lower core layer which have improved structures and which comprise improved magnetic materials.
It is another object of the present invention to provide a thin-film magnetic head which is suitable for higher recording densities and higher recording frequencies.
It is another object of the present invention to provide a method for making a thin-film magnetic head.
According to a first aspect of the present invention, a thin-film magnetic head includes a gap layer; a magnetic pole layer optionally provided on one face of the gap layer; a lower core layer; an upper core layer, the lower core layer and the upper core layer facing each other and being separated by the gap layer; and a coil layer for applying a recording magnetic field to the lower core layer and the upper core layer. At least one of the lower core layer and the upper core layer includes a soft magnetic layer and at least one high-specific-resistance layer formed on at least one of the upper face and the lower face of the soft magnetic layer, and the high-specific-resistance layer has a specific resistance which is higher than the specific resistance of the soft magnetic layer.
In the present invention, at least one of the lower core layer and the upper core layer includes the soft magnetic layer and at least one high-specific-resistance layer formed on at least one of the upper face and the lower face of the soft magnetic layer. This structure can reduce eddy current loss which is generated by increased recording frequencies. Thus, this thin-film magnetic head is suitable for future higher recording frequencies.
In the present invention, the high-specific-resistance layer is formed on the core layer, because eddy current loss is particularly generated in the vicinity of the core layer by skin effects.
Preferably, the high-specific-resistance layer is formed on the upper face of the upper core layer and is covered with a protective film. The protective film can prevent cracks of the high-specific-resistance layer which is generally formed of a fragile material.
Preferably, the protective film is formed of one of a NiFe alloy, elemental Ni, and a NiP alloy.
Preferably, the high-specific-resistance layer is formed at a portion other than a magnetic path-forming region toward the gap layer on at least one of the lower face of the upper core layer and the upper face of the lower core layer.
If the high-specific-resistance layer is formed in the magnetic path-forming region, a recording magnetic field generated in the vicinity of the gap is reduced. When the high-specific-resistance layer is formed on the upper face of the upper core layer or under the lower face of the lower core layer, such a limitation is unnecessary.
Preferably, the magnetic pole layer is a high Bs layer having a saturation magnetic flux density Bs which is higher than the saturation magnetic flux density Bs of the soft magnetic layer.
This configuration facilitates generation of a higher recording magnetic field in the vicinity of the gap. Thus, the thin-film magnetic head has improved recording resolution and is suitable for future higher recording densities.
In this configuration, the thin-film magnetic head preferably includes an insulating layer formed on the lower core layer, wherein the insulating layer has a groove having a width in the track width direction extending in the height direction from an opposing face opposing a recording medium, and the groove includes the high Bs layer and the gap layer therein.
This configuration is suitable in view of trends toward narrow track widths and is particularly suitable for a track width of 1.0 xcexcm or less and preferably 0.7 xcexcm or less. The high Bs layer formed in the groove can concentrate the recording magnetic field in the vicinity of the gap. As a result, higher recording densities can be achieved.
Preferably, the soft magnetic layer has a saturation magnetic flux density Bs which is higher than the saturation magnetic flux density Bs of the high-specific-resistance layer. The soft magnetic layer having a higher saturation magnetic flux density Bs can concentrate the recording magnetic field in the vicinity of the gap. As a result, higher recording densities can be achieved.
Preferably, the soft magnetic layer and the high-specific-resistance layer are composed of magnetic materials containing the same components including Fe in at least one of the upper core layer and the lower core layer, and the Fe content in the soft magnetic layer is higher than the Fe content in the high-specific-resistance layer.
Preferably, the soft magnetic layer and the high Bs layer are composed of magnetic materials containing the same components including Fe, and the Fe content in the high Bs layer is higher than the Fe content in the soft magnetic layer.
The increased Fe content causes an increased saturation magnetic flux density Bs.
Preferably, at least one of the soft magnetic layer, the high-specific-resistance layer, and the high Bs layer comprises a soft magnetic material having a composition which is represented by CoxFey and satisfies the relationships 20xe2x89xa6xxe2x89xa640 and 60xe2x89xa6yxe2x89xa680, or 86xe2x89xa6xxe2x89xa692, 8xe2x89xa6yxe2x89xa614, and x+y=100, wherein x and y represent Co and Fe contents, respectively, by atomic percent.
Preferably, at least one of the soft magnetic layer, the high-specific-resistance layer, and the high Bs layer comprises a soft magnetic material having a composition which is represented by CoxFeyNiz and satisfies the relationships 0.1xe2x89xa6xxe2x89xa615, 38xe2x89xa6yxe2x89xa660, 40xe2x89xa6zxe2x89xa662, and x+y+z 100, wherein x, y, and z represent Co, Fe, and Ni contents, respectively, by percent by weight.
Preferably, at least one of the soft magnetic layer, the high-specific-resistance layer, and the high Bs layer comprises a soft magnetic material having a composition which is represented by CoxFeyNizXw and satisfies the relationships 0.1xe2x89xa6xxe2x89xa615, 38xe2x89xa6yxe2x89xa660, 40xe2x89xa6zxe2x89xa662, 0.1xe2x89xa6w xe2x89xa63, and x+y+z+w=100, wherein x, y, z, and w represent Co, Fe, Ni, and X contents, respectively, by percent by weight, and X is at least one element selected from the group consisting of Mo, Cr, Pd, B, and In.
Preferably, at least one of the soft magnetic layer and the high Bs layer comprises the soft magnetic material.
Preferably, at least one of the soft magnetic layer, the high-specific-resistance layer, and the high Bs layer comprises a soft magnetic material having a composition which is represented by NixFey and satisfies the relationships 10xe2x89xa6xxe2x89xa670, 30xe2x89xa6yxe2x89xa690, and x+y=100 wherein x and y represent Ni and Fe contents, respectively, by atomic percent.
Preferably, at least one of the soft magnetic layer, the high-specific-resistance layer, and the high Bs layer comprises a soft magnetic material having a composition which is represented by FeaMbOc and satisfies the relationships 50xe2x89xa6axe2x89xa670, 5xe2x89xa6bxe2x89xa630, 10xe2x89xa6cxe2x89xa630, and a+b+c=100, wherein a, b, and c represent Fe, M, and O contents, respectively, by atomic percent, and M is at least one element selected from the group consisting of Hf, Zr, Ti, V, Nb, Ta, Cr. Mo, and W.
Preferably, the high-specific-resistance layer comprises the soft magnetic material.
Preferably, the high-specific-resistance layer comprises a soft magnetic material comprising Ni, Fe, and N and having an average crystal grain size of not more than 80 xc3x85, the Fe content being at least 30 percent by weight. In this case, the centerline average roughness (Ra) of the surface of the soft magnetic material is not more than 120 xc3x85.
Preferably, the high-specific-resistance layer comprises a soft magnetic material having a composition which is represented by NixFeyNbz, wherein x, y, and z indicates atomic percent and satisfy the relationships 76xe2x89xa6xxe2x89xa684, 8xe2x89xa6yxe2x89xa615, 5xe2x89xa6zxe2x89xa612, and x+y+z=100.
Preferably, the high-specific-resistance layer comprises one of NiFeP and FeNiPN.
Preferably, the soft magnetic layer and the high Bs layer comprise a soft magnetic material having a composition which is represented by CoxZryNbz and satisfies the relationships 1.5xe2x89xa6yxe2x89xa613, 6.5xe2x89xa6zxe2x89xa615, 1xe2x89xa6(y/z)xe2x89xa62.5, and x+y+z=100, wherein x, y, and.z represent Co, Zr, and Nb contents, respectively, by atomic percent.
Preferably, the soft magnetic layer and the high Bs layer comprise a soft magnetic material having a composition which is represented by CoxZryNbz and satisfies the relationships 1.5xe2x89xa6yxe2x89xa613, 6.5xe2x89xa6zxe2x89xa615, 1xe2x89xa6(y/z)xe2x89xa62.5, and x+y+z=100, wherein x, y, and z represent Co, Hf, and Nb contents, respectively, by atomic percent.
Preferably, at least one of the soft magnetic layer and the high Bs layer comprises a soft magnetic material having a composition comprising Fe as the major component, Co, and at least one element M selected from the group consisting of Hf, Zr, Ti, V, Nb, Ta, Cr, Mo, and W, the composition includes a crystalline phase primarily composed of Fe and a crystalline phase composed of carbides of the element M, and is composed of microcrystallites having an average crystal grain size of not more than 40 nm on the whole, wherein the ratio of the average crystal grain size d of the M carbides to the average crystal grain size D of the Fe crystalline phase is in a range of 0.05xe2x89xa6d/Dxe2x89xa60.4, and the composition is represented by the formula FexMyCz, wherein x, y, and z represents the Fe, M, and C contents by atomic percent, and satisfy the relationships 50xe2x89xa6xxe2x89xa696, 2xe2x89xa6yxe2x89xa630, 0.5xe2x89xa6zxe2x89xa625, and x+y+z=100.
Preferably, at least one of the soft magnetic layer and the high Bs layer comprises a soft magnetic material having a composition comprising at least one element T selected from Fe and Co as the major component, at least one element X selected from Si and Al, at least one element M selected from the group consisting of Ti, Zr, Hf, V, Ta, Mo, and W, at least one element Z selected from C and N, and at least one element Q selected from the group consisting of Cr, Re, Rh, Ni, Pd, Pt, and Au, the composition includes a crystalline.phase primarily composed of the element T, and a crystalline phase composed of at least one of carbide and nitride of the element M, and is composed of microcrystallites having an average crystal grain size of not more than 40 nm on the whole, wherein the ratio of the average crystal grain size d of the M carbide and the M nitride to the average crystal grain size D of the crystalline phase of the element T is in a range of 0.05xe2x89xa6d/Dxe2x89xa60.4, and the composition is represented by the formula TaXbMcZdQe, wherein a, b, c, d, and e represent atomic percent and satisfy the relationships 0xe2x89xa6bxe2x89xa625, 1xe2x89xa6cxe2x89xa610, 5xe2x89xa6dxe2x89xa615, 0xe2x89xa6exe2x89xa610, and a+b+c+d+e=100.
Preferably, at least one of the soft magnetic layer and the high Bs layer comprises a soft magnetic material having a composition comprising at least one element T selected from Fe and Co as the major component, Si, Al, at least one element M selected from the group consisting of Zr, Hf, Nb, and Ta, at least one element Z selected from C and N, and at least one element Q selected from the group consisting of Cr, Ti, Mo, W, V, Re, Ru, Rh, Ni, Pd, Pt, and Au, the composition includes a body centered cubic microcrystalline phase primarily composed of the element T and having an average crystal grain size of not more than 40 nm, wherein at least one element of Si and Al and the element Q are dissolved therein, and a crystalline phase of at least one of M carbide and M nitride which is precipitated at the grain boundaries of the microcrystalline phase, wherein the composition is represented by the formula TaSibAlcMdZeQf, wherein a, b, c, d, e, and f represent atomic percent and satisfy the relationships 8xe2x89xa6bxe2x89xa615, 0xe2x89xa6cxe2x89xa610, 1xe2x89xa6dxe2x89xa610, 1xe2x89xa6exe2x89xa610, 0xe2x89xa6fxe2x89xa615, and a+b+c+d+e+f=100.
Preferably, at least one of the soft magnetic layer and the high Bs layer comprises a soft magnetic material having a composition which is represented by the formula Ni1-xFex, and has an average crystal grain size of not more than 105 xc3x85, wherein the Fe content is in a range of 60 to 90 percent by weight. In this case, the centerline average roughness (Ra) of the surface of the soft magnetic film is preferably not more than 25 xc3x85.
According to a second aspect of the present invention, a method is provided for making a thin-film magnetic head, including a gap layer, the gap layer optionally having a magnetic pole layer, a lower core layer, an upper core layer, the lower core layer and the upper core layer facing each other and being separated by the gap layer, and a coil layer for applying a recording magnetic field to the lower core layer and the upper core layer. The method includes forming the soft magnetic layer when at least one of the lower core layer and the upper core layer is formed, and forming a high-specific-resistance layer having a specific resistance which is higher than that of the soft magnetic layer on at least one of the lower face and the upper face of the soft magnetic layer, by adding an amino-based organic material toxe2x89xa6a plating bath containing Fe and Ni ions so that a soft magnetic material containing Fe, Ni, and N is deposited.
In the present invention, the soft magnetic material contains nitrogen (N) as a tertiary component in addition to magnetic elements Fe and Ni. This tertiary component improves the specific resistance xcfx81 of the soft magnetic material. The thin-film magnetic head having a high-specific-resistance layer composed of this soft magnetic material exhibits reduced eddy current loss at future higher recording frequencies.
Preferably, the pH value of the plating bath is maintained at 1.8 or less.
Preferably, the amino-based organic material is at least one material selected from the group consisting of ethylenediamine (EDA), diethylenetriamine (DETA), triethylenetetramine (TETA), alanine (Ala), and glutamic acid (Glu).
Preferably, the soft magnetic layer of at least one of the lower core layer and the upper core layer comprises a NiFe alloy film, and the NiFe alloy film is formed by an electroplating process using a pulsed current.
The NiFe alloy formed by the electroplating process using the pulsed current exhibits an improved saturation magnetic flux density Bs. Thus, the thin-film magnetic head including a soft magnetic layer composed of this NiFe alloy is suitable for future higher recording densities.
Preferably, the NiFe alloy has a crystal grain size of not more than 105 xc3x85 and an Fe content in a range of 60 to 90 percent by weight. Preferably, the centerline average roughness (Ra) of the surface of the NiFe alloy film is not more than 25 xc3x85.